Waveguide for thermo optic device

ABSTRACT

A waveguide and resonator are formed on a lower cladding of a thermo optic device, each having a formation height that is substantially equal. Thereafter, the formation height of the waveguide is attenuated. In this manner, the aspect ratio as between the waveguide and resonator in an area where the waveguide and resonator front or face one another decreases (in comparison to the prior art) thereby restoring the synchronicity between the waveguide and the grating and allowing higher bandwidth configurations to be used. The waveguide attenuation is achieved by photomasking and etching the waveguide after the resonator and waveguide are formed. In one embodiment the photomasking and etching is performed after deposition of the upper cladding. In another, it is performed before the deposition. Thermo optic devices, thermo optic packages and fiber optic systems having these waveguides are also taught.

This application is a Divisional of U.S. application Ser. No.10/233,000, filed Aug. 29, 2002, now U.S. Pat. No. 7,706,746.

FIELD OF THE INVENTION

The present invention relates to thermo optic devices, such as opticalwaveguides. In particular, it relates to efficiently formed input andoutput waveguides having increased bandwidth.

BACKGROUND OF THE INVENTION

The art of making and developing new uses for thermo optic devicescontinues to emerge. Presently, thermo optic devices are used asfilters, switches, multiplexers, waveguides, and a host of othersemiconductor and optical transmission devices.

With reference to FIGS. 1A and 1B, a prior art thermo optic device inthe form of an optical waveguide is shown generally as 110. It comprisesa grating 112 formed of a lower cladding 114, an upper cladding 116, aninput waveguide 118, an output waveguide 120 and a grating waveguide andan optional resonator 122. As is known, the waveguides and resonator areformed of a material having a higher refractive index than that of theupper and lower claddings to propagate light therein during use. Thegrating 112 is disposed on a substrate 124. In many thermo optic devicesthe substrate is a printed circuit board or some form of silicon.

In forming the device, the lower cladding is deposited on the substrate.An intermediate layer, for the waveguides and resonator, is deposited onthe lower cladding, photo patterned and etched. The upper cladding isdeposited on the waveguides and resonator. In an alternate formationprocess, the lower cladding 206 is an oxidation of a silicon substratewith the waveguides, resonator and upper cladding being formed in thesame manner.

The inherent characteristics of waveguides and resonators, such as theirsizes, shapes, compositions, etc., may vary greatly from application toapplication. The characteristics of all waveguides and resonators,however, are generally selected in such a manner to eliminate crosstalkbetween the input and output waveguides at undesirable frequencies andto resonate signals (i.e., prolong and/or intensify) which allowstransfer between the waveguides at desirable frequencies. Theundesirable frequencies are not transferred between the two waveguides.The range of frequencies that are not transferred is determined by theproperties of the grating, and is typically referred to as thebandwidth. The frequencies that are transferred are determined by thespecific designs of the grating resonator waveguides.

In the representative prior art embodiment shown in FIG. 1B, theresonator 122 has a generally symmetrical tooth-shaped pattern. To setthe center frequency, the grating corrugation period is adjusted byadjusting the pitch (distance) between the teeth.

As part of the task of setting the bandwidth, an aspect ratio isadjusted in an area where the waveguide and resonator front or face oneanother. It is not possible to change the bandwidth by only changing theaspect ratio. The grating strength changes the bandwidth and it isnecessary to change the aspect ratio to allow the device to operateappropriately.

For example, in FIG. 1A, resonator 122 has a surface 123 facing asurface 119 of input waveguide 118. The aspect ratio (a.r.) in this areais defined as the area of the input waveguide surface to the area of theresonator surface (a.r.=area of input waveguide surface/area ofresonator surface). A large bandwidth corresponds to a small aspectratio while a small bandwidth corresponds to a large aspect ratio.Correspondingly, a large bandwidth can be achieved by either increasingthe area of the resonator surface, decreasing the area of the inputwaveguide surface, or adjusting both surface areas in such a manner toachieve a relatively small ratio number. A small bandwidth can beachieved by either decreasing the area of the resonator surface,increasing the area of the input waveguide surface, or adjusting bothsurface areas in such a manner to achieve a relatively large rationumber. Even further, increases or decreases of surface area can beachieved by adjusting one or both of the surface dimensions of thewaveguide or resonator surfaces. For example, depth “D” of surface 119or 123 may be increased or decreased according to desired bandwidth.

In other words, to set the bandwidth, the strength of the gratingbetween the input and output waveguides is increased. As the gratingstrength is increased, the difference in effective index for waveguideswith and without gratings becomes increasingly difficult to maintain.The difference in effective index for coupled devices such as these istypically referred to as asynchronicity. The term asynchronicityindicates that the propagation constant at the resonant wavelength isdifferent for the waveguide and grating, which limits the amount oflight that can be coupled between them. The problem of asynchronicitybecomes even more problematic when it is desirable to achievepolarization independent devices, as is required for commercial fiberoptic components. In this case, coupling between the grating andwaveguide requires synchronicity for both of the orthogonal polarizationstates of the system.

Methods for trimming the effective index of the waveguide to match thegrating, or grating to match the waveguide, are required to achieveoptimal performance from coupled systems such as the waveguide/gratingcoupler system. Trimming approaches have been defined elsewhere (See“Integrated-Optic Grating-Based Filters For Optical CommunicationSystems” by Jay Northrop Damask, Massachusetts Institute of Technologythesis, available Jul. 16, 1996, chapter 4), but are not generalized foraddressing arbitrary waveguide combinations, or are not compatible withstandard processing techniques.

Since the resonator 122 and the input and output waveguides 118, 120 areformed together during the same process steps as described above, thedepth, D, of the resonator is essentially fixed as the same depth of thewaveguides and therefore the asynchronicity limits the bandwidths andgrating strengths that can be used.

Accordingly, the thermo optic arts desire waveguides having increasedbandwidths that are relatively cheap and quick to produce withoutsacrifices in quality, reliability or longevity.

SUMMARY OF THE INVENTION

The above-mentioned and other problems become solved by applying theapparatus and method principles and teachings associated with thehereinafter described waveguide for thermo optic device.

In one embodiment, a waveguide and resonator are formed on a lowercladding of the thermo optic device, each having a formation height thatis substantially equal. Thereafter, the formation height of thewaveguide is attenuated. In this manner, the effective index between thewaveguide and grating can be matched, thereby allowing the synchronicityrequirements to be met for larger bandwidth devices. The waveguideattenuation is achieved by photomasking and etching the waveguide afterthe resonator and waveguide are formed. In one embodiment thephotomasking and etching is performed after deposition of the uppercladding. In another, it is performed before the deposition.

In another embodiment, a plurality of waveguides, an input and outputwaveguide, are attenuated from their respective formation heights to adifferent or substantially equal waveguide height. In still anotherembodiment, a plurality of resonators are formed between the input andoutput waveguides.

In still another embodiment, resonator(s) are attenuated before or afterdeposition of the upper cladding.

Thermo optic devices, thermo optic packages and fiber optic systemshaving these waveguides are also taught.

These and other embodiments, aspects, advantages, and features of thepresent invention will be set forth in part in the description whichfollows, and in part will become apparent to those skilled in the art byreference to the following description of the invention and referenceddrawings or by practice of the invention. The aspects, advantages, andfeatures of the invention are realized and attained by means of theinstrumentalities, procedures, and combinations particularly pointed outin the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross sectional view of a thermo optic device in the formof an optical waveguide in accordance with the prior art;

FIG. 1B is a planar view of the thermo optic device of FIG. 1A;

FIG. 2A is a cross sectional view of a lower cladding on which awaveguide in accordance with the teachings of the present invention willbe formed;

FIG. 2B is a cross sectional view in accordance with the teachings ofthe present invention of a first photomasking step in a processing stepsubsequent to FIG. 2A;

FIG. 2C is a cross sectional view in accordance with the teachings ofthe present invention of waveguides and resonators formed on a lowercladding in a processing step subsequent to FIG. 2B;

FIG. 2D is a cross sectional view in accordance with the teachings ofthe present invention of an upper cladding deposited on the waveguidesand resonator in a processing step subsequent to FIG. 2C;

FIG. 2E is a cross sectional view in accordance with the teachings ofthe present invention of a second photomasking step in a processing stepsubsequent to FIG. 2D;

FIG. 2F is a cross sectional view in accordance with the teachings ofthe present invention of an attenuated height waveguide in a processingstep subsequent to FIG. 2E;

FIG. 2G is a cross sectional view in accordance with the teachings ofthe present invention of an attenuated height waveguide in a processingstep subsequent to FIG. 2F;

FIG. 3 is a cross sectional view in accordance with the teachings of thepresent invention of an alternate embodiment of an attenuated heightwaveguide;

FIG. 4 is a cross sectional view in accordance with the teachings of thepresent invention of a plurality of attenuated height waveguides havingthe same height;

FIG. 5 is a cross sectional view in accordance with the teachings of thepresent invention of another embodiment of a plurality of attenuatedheight waveguides having different heights;

FIG. 6A is a cross sectional view in accordance with the teachings ofthe present invention of an alternate embodiment of a secondphotomasking step in a processing step subsequent to FIG. 2D;

FIG. 6B is a cross sectional view in accordance with the teachings ofthe present invention of an attenuated height waveguide in a processingstep subsequent to FIG. 6A;

FIG. 6C is a cross sectional view in accordance with the teachings ofthe present invention of an upper cladding formed on the waveguides andresonator in a processing step subsequent to FIG. 6B;

FIG. 7 is a cross sectional view in accordance with the teachings of thepresent invention of an alternate embodiment of an attenuated heightwaveguide;

FIG. 8 is a cross sectional view in accordance with the teachings of thepresent invention of a plurality of attenuated height waveguides havingthe same height;

FIG. 9 is a cross sectional view in accordance with the teachings of thepresent invention of another embodiment of a plurality of attenuatedheight waveguides having different heights;

FIG. 10 is a cross sectional view in accordance with the teachings ofthe present invention of an attenuated height resonator;

FIG. 11 is a cross sectional view in accordance with the teachings ofthe present invention of another embodiment of an attenuated heightresonator;

FIG. 12A is a cross sectional view in accordance with the teachings ofthe present invention of waveguides and a resonator formed on a lowercladding;

FIG. 12B is a cross sectional view in accordance with the teachings ofthe present invention of an attenuated height input waveguide, anattenuated height output waveguide and an attenuated height resonatorall having different heights;

FIG. 13 is a cross sectional view in accordance with the teachings ofthe present invention of an attenuated height waveguide coupled to anoutput waveguide via a plurality of resonators;

FIG. 14 is a block diagram of a system having a thermo optic packagecomprising waveguides formed in accordance with the teachings of thepresent invention; and

FIG. 15 is an alternative embodiment of a thermo optic packagecomprising waveguides formed in accordance with the teachings of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings which form a part hereof,and in which is shown by way of illustration, specific embodiments inwhich the inventions may be practiced. These embodiments are describedin sufficient detail to enable those skilled in the art to practice theinvention, and it is to be understood that other embodiments may beutilized and that process, electrical or mechanical changes may be madewithout departing from the scope of the present invention. The termsubstrate used in this specification includes any base semiconductorstructure such as silicon-on-sapphire (SOS) technology,silicon-on-insulator (SOI) technology, thin film transistor (TFT)technology, doped and undoped semiconductors, epitaxial layers of asilicon supported by a base semiconductor structure, as well as othersemiconductor structures well known to one skilled in the art. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present invention is defined onlyby the appended claims and their equivalents.

The following description and figures use a reference numeral conventionwhere the first digit of the reference numeral corresponds to the figureand the following two digits correspond to like elements throughout thespecification. For example, the lower cladding of a thermo optic deviceof the present invention has a reference number of 202, 302, 402, etc.corresponding to the lower cladding X02 in FIGS. 2, 3, 4, etc. where Xis the number of the figure in which the reference numeral appears.

For definition purposes: a “formation height,” either waveguide orresonator, is a height before any attenuation is performed to astructure and is to be distinguished from a resonator “height” orwaveguide “height” which is the height of a structure after someattenuation has been performed. In other words, the two words “formationheight” will be used to identify heights of structures pre-attenuationand the single word “height” will be used to identify structurespost-attenuation. For example, in the event a structure itself was notattenuated, its “formation height” will be the same as its “height”after another structure has been attenuated, i.e., the resonatorformation height in FIG. 2C is the same as the resonator height in FIG.2F. In contrast, in the event a structure has been attenuated, its“formation height” will be taller than its “height” after attenuation,i.e., the input waveguide formation height of FIG. 2C is taller than theinput waveguide height of FIG. 2F.

With reference to FIG. 2A, a substrate 200 is provided upon which awaveguide for use with a thermo optic device will be formed. In oneembodiment the substrate is silicon. In another, it is a printed circuitboard. In still another, it is any surface upon which a layer may bedeposited.

A first layer 202 or lower cladding is formed on the substrate. In oneembodiment, the substrate is some form of silicon and the first layer isa grown layer via oxidation of the substrate. In another embodiment, thefirst layer is a deposited layer.

Some techniques for depositing the first layer, and all remainingdeposited layers, include, but are not limited to, any variety ofchemical vapor depositions (CVD), physical vapor depositions (PVD),epitaxy, evaporation, sputtering or other known or hereinafter developedtechniques. Specific CVD techniques include low pressure (LP) ones, butcould also be atmospheric pressure (AP), plasma enhanced (PE), highdensity plasma (HDP) or other.

In still another embodiment, the first layer is a silicon oxide that isdeposited via a LPCVD technique using a tetraethyl orthosilicate or TEOSsource.

After depositing the first layer, a second layer 204 is deposited on thefirst layer using one of the above or other deposition techniques. Inone embodiment, the second layer is a silicon oxynitride deposited witha PECVD technique using a silane with nitrous oxide reaction in an argonor helium plasma, under the conditions of 450° C., 450 watts and 13.56MHz. In another embodiment, the second layer is a translucent material.

While the lower cladding, in one embodiment, was formed of a siliconoxide and the second layer was formed of silicon oxynitride, it shouldbe appreciated that numerous other materials for these first and secondlayers exist. One skilled in the art will understand that a variety ofanneal steps can follow the above steps.

The selection of the layers is dictated by the index of refraction,absorption in the wavelength range of interest, thermo-opticcoefficients and other optical and mechanical properties. The secondlayer will be formed into the waveguide and grating and light willpropagate there by virtue of total internal reflection of light. So longas the second layer is a material having an index of refraction that ishigher than the index of refraction of the first layer at the wavelengthof interest, light signals will be guided and propagated in the device.

In FIG. 2B, a first mask 206 is provided to photo impact 208 the secondlayer 204 in a photomasking step thereby producing a photo impactedregion 210 in the second layer on top of the lower cladding.

In one embodiment, the photo impacting is accomplished with anultraviolet light from a photolithography device well known to thoseskilled in the art. The photo impacting, however, should not be limitedto such an embodiment and may alternatively include X-rays or otherlight sources.

The first mask 206 may be configured as a clear-field or dark-fieldmask, as those terms as well understood by skilled artisans, accordingto the desired design of the photo impacted region 210 in the secondlayer.

Thereafter, with reference to FIG. 2C, the second layer 204 is etched sothat the photo impacted region 210 remains thereby leaving or forming awaveguide and resonator on the surface 220 of the lower cladding, firstlayer 202. In particular, an input waveguide 212, an output waveguide214 and a resonator 216, between the input and output resonators tocouple light signals from the input to the output during use, are formedon the surface 220. Each of the waveguides and resonator have aformation height that is substantially equal since they were formedtogether in the same process. This height is measured from the surface220 of the first layer 202 to plane 218. Although no particularformation height is required for this invention, for reference purposes,the formation height is often about 1 to about 2 microns. The heightdepends upon the particular application in which the thermo optic devicewill be used and the optical properties of the layers.

Some particular etching techniques embraced by this invention forforming the waveguides and resonators by leaving the photo impactedregion 210 on the lower cladding include, but are not limited to, anyvariety of wet etches including immersion or spray, or dry etchesincluding plasma, barrel or planar, ion milling, reactive ion etches(RIE) or deep RIE.

In one particular embodiment of the invention, the second layer is dryetched with a photo resist pattern and CF₄ or CF₄CHF₃ Argon basedchemistry in a parallel plate reactor under the conditions of about 50militorr, 600 watts and 13.56 MHz.

With reference to FIG. 2D, a third layer 22 or upper cladding isdeposited on the surface of the waveguides 212, 214 and the resonator216 and portions of the first layer 202 not having such structuresformed thereon. The upper cladding is deposited to a thicknesssufficient to prevent external fields and circuitry from interferingwith the light propagated n the waveguide during use. For referencepurposes only, the upper cladding are, in one embodiment, deposited tothe same thickness of about 4 microns nominally.

In another embodiment, the third layer is a second silicon oxide layerdeposited in the same manner as previously described for the firstlayer. In still another embodiment, the third layer has an index ofrefraction that is substantially equal to the index of refraction of thefirst layer.

It will be appreciated that the third layer 222 has an upper surfacethat can be used to stack multiple thermo optic devices by continuingthe deposition, patterning and etching processes described herein. Theupper surface may alternatively contain a heater (not shown) forchanging a thermo optical property of the device as light propagates inthe waveguide during use.

With reference to FIG. 2E, after depositing the third layer 222, asecond mask 224 is provided to attenuate the top of a waveguide as shownin FIG. 2F. In particular, the top 226 of input waveguide 212 isattenuated a height, H, from the top 228 of the resonator 216 by meansof etching, especially dry etching.

Many things should now be apparent to those skilled in the art. Forexample, the input waveguide has a waveguide height that is shorter thanthe resonator height while the output waveguide remains the same heightas the resonator height which is the same as their respective formationheights. As a result, the aspect ratio between the resonator and theinput waveguide has decreased (in comparison to the prior art, FIG. 1A,for example) thereby maintaining the synchronicity condition.

In particular, the aspect ratio (a.r.) in area 213 has decreased wherethe input waveguide 212 and resonator 216 front one another alongresonator surface 217 and input waveguide surface 211, wherein (a.r.) inarea 213 is defined as the area of the input waveguide surface 211 tothe area of the resonator surface 217 or (a.r.=area of input waveguidesurface 211/area of resonator surface 217).

The resonator height from the surface 220 to the top 228 of theresonator 216, like the input or output waveguide height from surface220 to top 226 or top 227 of the input waveguide 21 or output waveguide214, respectively, is not required to be any particular height and isdictated according to the frequency characteristics demanded by theparticular application in which the thermo optic device is used. Forreference purposes, however, each of the heights can be found in a rangefrom about 1 to about 2 microns in one embodiment.

In still a similar manner, the horizontal spacing (as viewed in thefigure from left-to-right) between the grating and the waveguides, andlength over which the grating and waveguides couple to each other, isdetermined by the performance requirements of the device. For referencepurposes, however, the resonator is separated from the waveguide in oneembodiment in a range from about 1 to about 2 microns.

To complete one embodiment of the thermo optic device, a fourth layer250 may be deposited on the attenuated waveguide, the input waveguide,and the upper cladding, third layer 222. The fourth layer, like theupper cladding is deposited to a thickness sufficient to prevent outsidelight from interfering with the light propagated in the waveguide duringuse.

In one embodiment, the fourth layer is a third silicon oxide layerdeposited in the same manner as previously described for the thirdlayer. In another embodiment, the fourth layer has an index ofrefraction that is substantially equal to the index of refraction of thefirst and third layers.

It will be appreciated that the fourth layer 250 has an upper surfacethat can be used to stack multiple thermo optic devices by continuingthe deposition, patterning and etching processes described herein. Theupper surface may alternatively contain a heater (not shown) forchanging a thermo optical property of the device as light propagates inthe waveguide during use.

With reference to FIG. 3, it will be appreciated that a reciprocalembodiment of the one shown in FIG. 2F can be achieved with respect tothe output waveguide. In particular, the output waveguide 314 isattenuated in height from its formation height, which was substantiallythe same as the top 328 of the resonator 316, to the top 327. The inputwaveguide 312 remains the same height as the resonator.

Correspondingly, in area 315, the aspect ratio has decreased (incomparison to the prior art, FIG. 1A, for example) where the outputwaveguide 314 and resonator 316 front one another along resonatorsurface 319 and output waveguide surface 321, wherein (a.r.) in area 315is defined as the area of the output waveguide surface 321 to the areaof the resonator surface 319 or (a.r.=area of output waveguide surface321/area of resonator surface 319). As such, synchronicity between theoutput waveguide and the grating has been achieved, even for highbandwidth gratings.

In FIG. 4, both the input and output waveguides 412, 414 have beenattenuated in height, H1 and H2, respectively, where H1 is measured fromthe top 428 of the resonator to the top 426 of the input waveguide andH2 is measured from the top 428 of the resonator to the top 427 of theoutput waveguide 414. It will be appreciated that the resonator heightfrom the lower cladding to the top 428 of the resonator 416 is the sameheight as the resonator formation height (FIG. 2C, for example) becausethe resonator has not been attenuated. In the embodiment shown, H1 issubstantially equal to H2.

In FIG. 5, both the input and output waveguides are attenuated but areattenuated to different heights. In this embodiment, H1 is taller thanH2.

With reference to FIGS. 6A through 6C, it will be appreciated that theattenuation of a waveguide, in another embodiment, can occur before thedeposition of the upper cladding layer. In particular, a second mask 624masks resonator 616 and output waveguide 614 on the surface 620 of thelower cladding 602 so that the input waveguide 612 may be attenuated inheight via an etching process similar to the process steps of FIGS. 2Eand 2F before deposition of the upper cladding. As a result, the inputwaveguide is attenuated in height, H, as defined from the top 628 of theresonator 616 to the top 626 of the input waveguide 612.

To complete the thermo optic device, an upper cladding 622 is thendeposited on the surface of the waveguides 612, 614 and resonator 616and portions of the first layer 602 or lower cladding not having suchstructures formed thereon. As before, the upper cladding is deposited toa thickness sufficient to prevent external films and circuitry frominterfering with the light propagated in the waveguide during use. Theupper cladding may still have a resistive heater or other thermo opticdevices formed on an upper surface thereof as the application demands inwhich the device is to be used.

The input waveguide still has a waveguide height that is shorter thanthe resonator height while the output waveguide remains the same heightas the resonator height which is the same as their respective formationheights. Like before, the aspect ratio of the resonators and the inputwaveguide has been altered to maintain synchronicity and allow higherbandwidth devices to be used.

In particular, the aspect ratio (a.r.) in area 613 has decreased wherethe input waveguide 612 and resonator 616 front one another alongresonator surface 617 and input waveguide surface 611, wherein (a.r.) inarea 613 is defined as the area of the input waveguide surface 611 tothe area of the resonator surface 617 or (a.r.=area of input waveguidesurface 611/area of resonator surface 617).

In FIG. 7, in another embodiment of waveguide attenuation beforedeposition of the upper cladding, it is the output waveguide 714 that isattenuated in height, not the input waveguide 712. The aspect ratio(a.r.) in area 715 has decreased where the output waveguide 714 andresonator 716 front one another along resonator surface 719 and outputwaveguide surface 721, wherein (a.r.) in area 715 is defined as the areaof the output waveguide surface 721 to the area of the resonator surface719 or (a.r.=area of input waveguide surface 721/area of resonatorsurface 719).

With reference to FIG. 8, in still another embodiment of attenuating thewaveguide before deposition of the upper cladding, both the input andoutput waveguides 812, 814 have been attenuated. In particular, theyhave been attenuated a height H1 and H2, respectively, wherein H1 spansthe distance from the top 828 of resonator 816 to the top 828 of theinput waveguide and H2 spans the distance from the top 828 of resonator816 to the top of the output waveguide 827. As shown, H1 issubstantially equal or the same as H2. Correspondingly, the aspectratios in areas 813 and 815 have decreased (in comparison to the priorart) where synchronicity can be maintained for higher bandwidth devices.In FIG. 9, a view similar to FIG. 8, H1 is less than H2.

While the foregoing teaches thermo optic devices where synchronicity isachieved by attenuating a height of the waveguides, in an alternateembodiment of the present invention, it may be desirable to attenuate adimension of the grating to limit synchronicity.

For example, in FIGS. 10 and 11, it is the resonator having anattenuated height, not the waveguides. In particular, in FIG. 10, theresonator 1016 is attenuated in height from its formation height, whichwas substantially co-equal with the top 1026 of the input waveguide 1012and the top 1027 of the output waveguide, to the top 1028. The uppercladding 1022, in this embodiment, is formed on the resonator,waveguides and lower cladding 1002 after the resonator is attenuatedfrom its resonator formation height.

In FIG. 11, the upper cladding 1122 is formed on the resonator 1116, theinput waveguide 1112, the output waveguide 1114 and the lower cladding1102 before the resonator 1116 is attenuated in height to top 1128 fromits formation height which was substantially equal to top 1126 and 1127of the input and output waveguides, respectively.

It should be appreciated that even further embodiments of the presentinvention include attenuating the heights of all the waveguides and theresonator and attenuating them to different heights. For example, inFIGS. 12A and 12B, a resonator 1216 and a plurality of waveguides, inputwaveguide 1212 and output waveguide 1214, are formed on a lowercladding, first layer 1202 in accordance with the previously describedtechniques. Each has a formation height, H, which is substantially equaland spans the distance from the surface 1220 of the lower cladding totheir respective top surfaces, 1228, 1226 and 1227.

After attenuation (FIG. 12B), the resonator 1216 has a resonator height,H3, shorter than its formation height and spans the distance from thesurface 1220 to top 1228. The input waveguide 1212 has an inputwaveguide height, H2, shorter than its formation height and spans thedistance from the surface 1220 to top 1226. The output waveguide 1227has an output waveguide height, H3, shorter than its formation heightand spans the distance from the surface 1220 to top 1227. As shown, H3is greater than H2 which is greater than H1. It should be appreciated,however, that the heights could all be variously arranged so that thewaveguides are taller than the resonator or that the output waveguide isthe tallest, etc. As with previous embodiments, these attenuatedstructures could be attenuated before or after the deposition of anupper cladding layer, not shown.

In FIG. 13, it will be appreciated that thermo optic devices of thepresent invention may be formed with a more than a single resonator toachieve even further variations in the frequency characteristics of thedevice as application demand varies. In particular, a plurality ofresonators 1328A and 1328B are formed on a surface 1320 of the lowercladding between the input and output waveguides 1312, 1314, to couple alight signal from the input to the output waveguide during use. Aspreviously described for single resonator embodiments, the plurality ofresonators are formed in the same process steps as the waveguides andare formed of the second material. Each resonator has a formation heightthat is substantially equal with the waveguides when formed. After theinput waveguide is attenuated, as shown in this embodiment, the inputwaveguide is shorter than either of the resonators and output waveguide.In particular, it is shorter by distance, H, spanning from the top 1328Aand 1328B to the top 1326 of the input waveguide 1312. The outputwaveguide 1314 has a top 1327 that is substantially equal to the top1328 of the resonators. It will be appreciated, that the pluralities ofresonators may also be attenuated in accordance with previously shownsingle resonator embodiments. Likewise, the output waveguide may also beattenuated from its formation height. All embodiments may attenuateheights before or after the deposition of an upper cladding, not shown.Those skilled will appreciate that still other numbers of resonators,beyond the two shown, could be formed.

With reference to FIG. 14, a system, having as part thereof a resonatoror waveguide formed in accordance with the teachings of the presentinvention, is shown generally as 1441. The system may be an exclusivelyfiber optic system or may be a system having other software and hardwaredevices, as indicated by the dashed line 1445, operably coupled to atleast one fiber optic component thereof.

In either system, a light source 1443 will be provided as the source forpropagating light signals along at least one fiber optic line 1447. Wellknown light sources include, but are not limited to, laser lightsources. In the embodiment shown, the system 1441 includes a pluralityof fiber optic lines 1447.

Coupleable to the fiber optic lines via a plurality of input fiber opticports 1451 is a thermo optic package 1449. Contained within the thermooptic package is at least one thermo optic device 1453 having at leastone waveguide or resonator formed in accordance with the presentinvention. In the embodiment shown, the thermo optic device 1453 iscoupled to the input fiber optic port 1451 via an input connector 1455while an output connector 1457 couples the thermo optic device to anoutput fiber optic port 1459. In turn, the output fiber optic port 1459is coupled to another fiber optic line 1447 of system 1441.

During use, a system user merely needs to couple fiber optic lines 1447to the input and output fiber optic ports of the package 1449 to readilyachieve at least one resonator or waveguide having an increased ordecreased bandwidth as necessary.

With reference to FIG. 15, an alternative embodiment of a thermo opticpackage 1549 is shown having a thermo optic device 1553 with a singleinput connector 1555 and a plurality of output connectors 1557. Theinput connector 1555 connects with input fiber optic port 1551 which isreadily matable with a fiber optic line 1547 of a system. The outputconnectors 1557 of thermo optic device 1553 are each matable with anoutput fiber optic port 1559.

It will be appreciated that while shown as a single input connector withtwo output connectors, the thermo optic device 1553 having a resonatoror waveguide formed in accordance with the present invention mayalternatively have two or more input connectors and one or more outputconnectors depending upon the type and desired use of the thermo opticdevice 1553.

CONCLUSION

The above structures and fabrication methods have been described, by wayof example, and not by way of limitation, with respect to waveguides forthermo optic devices.

In particular, a waveguide and resonator are formed in the same processsteps on a lower cladding of the thermo optic device and each have aformation height that is substantially equal. Thereafter, the formationheight of the waveguide is attenuated. In this manner, the aspect ratioas between the waveguide and resonator in an area where the waveguideand resonator front or face one another decreases (in comparison to theprior art) thereby restoring the synchronicity between the waveguide andthe grating and allowing higher bandwidth configurations to be used. Thewaveguide attenuation is achieved by photomasking and etching thewaveguide after the resonator and waveguide are formed. In oneembodiment the photomasking and etching is performed after deposition ofthe upper cladding. In another, it is performed before the deposition.

In another embodiment, a plurality of waveguides, an input and outputwaveguide, are attenuated from their respective formation heights to adifferent or substantially equal waveguide height. In still anotherembodiment, a plurality of resonators are formed between the input andoutput waveguides.

In still another embodiment, resonator(s) are attenuated before or afterdeposition of the upper cladding. In this manner, the aspect ratioincreases thereby decreasing the available signal bandwidth.

Thermo optic devices, thermo optic packages and fiber optic systemshaving these waveguides are also taught.

As a result, waveguides of this invention can be formed quicker andcheaper without any corresponding sacrifice in quality, reliability orlongevity.

The present invention has been particularly shown and described withrespect to certain preferred embodiment(s). However, it will be readilyapparent to those of ordinary skill in the art that a wide variety ofalternate embodiments, adaptations or variations of the preferredembodiment(s), and/or equivalent embodiments may be made withoutdeparting from the intended scope of the present invention as set forthin the appended claims. Accordingly, the present invention is notlimited except as by the appended claims.

1. A method, comprising: forming a lower cladding; forming a waveguideon the lower cladding, the waveguide having a waveguide formationheight; and attenuating the waveguide formation height to reduce theformation height to a waveguide height that is less than the formationheight, wherein a difference between the waveguide formation height andthe waveguide height is less than the waveguide formation height.
 2. Themethod according to claim 1, further including forming a resonator onthe lower cladding, the resonator having a resonator formation heightsubstantially equal to the waveguide formation height.
 3. The methodaccording to claim 1, further including forming another waveguide on thelower cladding, the another waveguide having an another waveguideformation height substantially equal to the waveguide formation height.4. The method according to claim 1, wherein the attenuating thewaveguide formation height further includes dry etching the waveguide.5. A method, comprising: forming a lower cladding; forming an input andan output waveguide on the lower cladding, the input and outputwaveguides each having a waveguide formation height; and attenuating thewaveguide formation height of one of the input waveguides and the outputwaveguides to reduce the formation height to a waveguide height that isless than the formation height, wherein a difference between thewaveguide formation height and the waveguide height is less than thewaveguide formation height.
 6. The method according to claim 5, furtherincluding forming a resonator on the lower cladding, the resonatorhaving a resonator formation height substantially equal to the waveguideformation height.
 7. The method according to claim 5, further includingforming an upper cladding on the input and output waveguides.
 8. Themethod according to claim 7, wherein the attenuating the waveguideformation height further includes etching one of the input and outputwaveguides.
 9. A method, comprising: forming a lower cladding; forming aplurality of waveguides on the lower cladding, each of the waveguideshaving a waveguide formation height; forming a resonator on the lowercladding, the resonator having a resonator formation height; andattenuating the waveguide formation height of each of the plurality ofwaveguides to reduce the formation height to a wave guide height that isless than the formation height wherein a difference between thewaveguide formation height and the waveguide height is less than thewaveguide formation height.
 10. The method according to claim 9, whereinthe attenuating the waveguide formation height further includes maskingthe plurality of waveguides.
 11. The method according to claim 10,wherein the attenuating the waveguide formation height further includesetching the plurality of waveguides.
 12. The method according to claim9, wherein the forming the waveguides and resonator on the lowercladding further includes masking a second layer formed on the lowercladding.
 13. The method according to claim 12, wherein the forming thewaveguides and resonator on the lower cladding further includes photoimpacting the second layer to form a photo impacted region.
 14. Themethod according to claim 13, wherein the forming the waveguides andresonator on the lower cladding further includes etching the secondlayer.
 15. A method, comprising: depositing a first layer on asubstrate; depositing a second layer on the first layer; masking thesecond layer; photo impacting the second layer to form a photo impactedregion therein; etching the second layer to form a plurality ofwaveguides and a resonator on the first layer, each of the waveguideshaving a waveguide formation height, the resonator having a resonatorformation height, the waveguide formation heights and the resonatorformation height being substantially equal; masking one of thewaveguides; and etching the one of the waveguides to form an attenuatedwaveguide having a height less than the waveguide formation height suchthat a difference between the waveguide formation height and thewaveguide height is less than the waveguide formation height.
 16. Themethod according to claim 15, further including depositing a third layeron the plurality of waveguides and the resonator.
 17. The methodaccording to claim 16, further including depositing a fourth layer onthe attenuated waveguide.
 18. The method according to claim 15, whereinthe depositing the second layer on the first layer further includesselecting the second layer to have an index of refraction that is lowerthan an index of refraction of the first layer.
 19. A method of forminga thermo optic device, comprising: providing a substrate; forming alower cladding on the substrate; forming an input and output waveguideon the lower cladding, the input and output waveguides each having awaveguide formation height; forming a plurality of resonators on thelower cladding between the input and output waveguides to couple a lightsignal from the input waveguide to the output waveguide during use, eachof the resonators having a resonator formation height; attenuating oneof the waveguide formation heights and resonator formation heights toreduce the formation height to an attenuated height that is less thanthe formation height, wherein a difference between the one of thewaveguide formation heights and the resonator formation heights and theattenuated height is less than the waveguide formation heights and theresonator formation heights; and forming an upper cladding on the inputand output waveguides and the plurality of resonators.
 20. The methodaccording to claim 19, wherein the attenuating one of the waveguideformation heights and resonator formation heights further includesmasking one of the input and output waveguides and the plurality ofresonators.
 21. The method according to claim 19, wherein the formingthe input and output waveguides and the plurality of resonators on thelower cladding further includes forming the input and output waveguidesand the plurality of resonators with a material having an index ofrefraction that is lower than an index of refraction of the lowercladding.
 22. The method according to claim 19, wherein the forming anupper cladding further includes forming the upper cladding with amaterial having an index of refraction that is lower than an index ofrefraction of the input and output waveguides and the plurality ofresonators.
 23. A method of forming a thermo optic device, comprising:providing a substrate; forming a lower cladding on the substrate;forming an input and output waveguide on the lower cladding, the inputand output waveguides each having a waveguide formation height; forminga resonator on the lower cladding between the input and outputwaveguides to couple a light signal from the input waveguide to theoutput waveguide during use, the resonator having a resonator formationheight; masking one of the input and output waveguides; and etching theone of the input and output waveguides to form an attenuated waveguidehaving an attenuated height less than the waveguide formation height,such that a difference between the waveguide formation height and theattenuated height is less than the waveguide formation height.
 24. Themethod according to claim 23, further including forming an uppercladding on the input and output waveguides and the plurality ofresonators.
 25. A thermo optic device formed according to the method ofclaim
 23. 26. The method according to claim 15, wherein the depositingthe second layer on the first layer further includes selecting thesecond layer to have an index of refraction that is higher than an indexof refraction of the first layer.
 27. The method according to claim 19,wherein the forming the input and output waveguides and the plurality ofresonators on the lower cladding further includes forming the input andoutput waveguides and the plurality of resonators with a material havingan index of refraction that is higher than an index of refraction of thelower cladding.
 28. The method according to claim 19, wherein theforming an upper cladding further includes forming the upper claddingwith a material having an index of refraction that is higher than anindex of refraction of the input and output waveguides and the pluralityof resonators.
 29. A method, comprising: forming a lower cladding;forming an input waveguide and an output waveguide on the lowercladding, the input waveguide and the output waveguide having a firstheight; selecting one of the input waveguide and the output waveguide;and altering the selected one of the input waveguide and the outputwaveguide to reduce the first height to a second height that is lessthan the first height, wherein the second height is greater than zero.30. The method of claim 29, further comprising forming a resonator onthe lower cladding that is positioned between the input waveguide andthe output waveguide, the resonator having the first height.
 31. Themethod of claim 30, further comprising selecting the resonator; andaltering the resonator to reduce the first height to the second height,wherein the second height is greater than zero.
 32. The method of claim30, further comprising selecting the resonator; and altering theresonator to reduce the first height to a third height that is differentfrom the second height, wherein the third height is greater than zero.33. The method of claim 29, wherein altering the selected one of theinput waveguide and the output waveguide to reduce the first height to asecond height further comprises dry etching the selected one of theinput waveguide and the output waveguide.
 34. The method of claim 29,further comprising forming an upper cladding on the input waveguide andthe output waveguide.
 35. The method of claim 34, further comprisingforming a heating element on the upper cladding that is configured toalter an optical property of the input waveguide and the outputwaveguide.
 36. The method of claim 29, further comprising providing asupporting substrate that underlies the lower cladding.
 37. A method,comprising: forming a lower cladding; forming an input waveguide and anoutput waveguide spaced apart from the input waveguide on the lowercladding, the input waveguide and the output waveguide having a firstheight; forming a resonator between the input waveguide and the outputwaveguide, the resonator having the first height; selecting one of theinput waveguide, the output waveguide and the resonator and reducing theselected one of the input waveguide, the output waveguide and theresonator from the first height to a second height that is less than thefirst height and greater than zero; and selecting another one of theinput waveguide, the output waveguide and the resonator and reducing theselected another one of the input waveguide, the output waveguide andthe resonator from the first height to a third height that is differentthan the first height and the second height, wherein the third height isgreater than zero.
 38. The method of claim 37, further comprisingselecting a remaining one of the input waveguide, the output waveguideand the resonator and reducing the remaining one of the input waveguide,the output waveguide and the resonator from the first height to a fourthheight that is different than the first height, the second height andthe third height, wherein the fourth height is greater than zero. 39.The method of claim 37, further comprising forming an upper cladding onthe input waveguide, the output waveguide and the resonator.
 40. Themethod of claim 39, further comprising forming a heating element on theupper cladding that is configured to alter an optical property of theinput waveguide, the output waveguide and the resonator.
 41. The methodof claim 37, further comprising providing a supporting substrate thatunderlies the lower cladding.
 42. A method, comprising: forming a lowercladding; forming a plurality of waveguides on the lower cladding, eachof the waveguides having a uniform height; selecting a portion of theplurality of waveguides; and altering the uniform height of the portionof the plurality of waveguides to reduce the uniform height to at leastone reduced height that is less than the uniform height and greater thanzero.
 43. The method of claim 42, wherein selecting a portion of theplurality of waveguides further comprises photomasking the portion ofthe plurality of waveguides.
 44. The method of claim 42, whereinaltering the uniform height of the portion of the plurality ofwaveguides further comprises etching the portion of the plurality ofwaveguides.
 45. The method of claim 42, further comprising forming aresonator on the lower cladding having the uniform height.
 46. Themethod of claim 45, further comprising selecting the resonator; andaltering the uniform height of the resonator to reduce the uniformheight to a reduced height that is less than the uniform height andgreater than zero.
 47. The method of claim 45, further comprisingforming an upper cladding on the plurality of waveguides and theresonator.
 48. The method of claim 47, further comprising forming aheating element on the upper cladding that is configured to alter anoptical property of the plurality of waveguides and the resonator. 49.The method of claim 42, further comprising providing a supportingsubstrate that underlies the lower cladding.
 50. A method, comprising:depositing a homogeneous first layer having a first index of refractionon a substrate; depositing a homogeneous second layer having a secondindex of refraction that is different from the first index of refractionon the first layer; masking the second layer; exposing the second layerto a radiation source to form a plurality of photo impacted regions inthe second layer; etching the second layer to form a plurality ofwaveguides and a resonator on the first layer, the plurality ofwaveguides and the resonator extending outwardly from the first layer toa first height; masking a selected waveguide; and etching the selectedwaveguide to reduce the selected waveguide from the first height to asecond height that is greater than zero and less than, but not equal tothe first height.
 51. The method of claim 50, further comprisingdepositing a third layer on the plurality of waveguides and theresonator.
 52. The method of claim 51, further comprising depositing afourth layer on the third layer and onto the selected waveguide.
 53. Themethod of claim 50, further comprising: selecting the first layer toinclude a material having a first index of refraction; selecting thesecond layer to include a material having a second index of refractionthat is less than the first index of refraction.
 54. The method of claim53, wherein the first layer includes an oxide of silicon deposited usinga TEOS precursor, and the second layer includes a translucent material.55. The method of claim 53, wherein the second layer includes siliconoxynitride.
 56. A method, comprising: providing a substrate; forming alower cladding on the substrate from an optically homogeneous material;forming an optically continuous input waveguide and an opticallycontinuous output waveguide having a first height on the lower cladding;forming at least one optically continuous resonator having the firstheight on the lower cladding between the input waveguide and the outputwaveguide to couple a light signal from the input waveguide to theoutput waveguide; selecting one or more of the input waveguide, theoutput waveguide and the at least one resonator; etching the selectedone of the input waveguide, the output waveguide and the at least oneresonator to reduce the selected one of the input waveguide, the outputwaveguide and the at least one resonator from the first height to asecond height that is greater than zero and less than, but not equal tothe first height; and forming an upper cladding on the input and outputwaveguides and the at least one resonator.
 57. The method of claim 56,wherein etching the selected one of the input waveguide, the outputwaveguide and the at least one resonator further comprises masking theselected one of the input waveguide, the output waveguide and the atleast one resonator.
 58. The method of claim 56, wherein the forming alower cladding further comprises forming the lower cladding with amaterial having a first index of refraction, and further wherein formingan upper cladding further comprises forming the upper cladding with amaterial having a second index of refraction, the first index ofrefraction being different from the second index of refraction.
 59. Amethod, comprising: providing a substrate; forming a lower cladding onthe substrate, the lower cladding having a first index of refraction;forming an input waveguide and an output waveguide on the lower claddinghaving a second index of refraction and extending to a first height;forming a resonator on the lower cladding having the second index ofrefraction and positioned between the input waveguide and the outputwaveguides to couple a light signal from the input waveguide to theoutput waveguide, the resonator extending to the first height;selectively masking one of the input waveguide and the output waveguide;and etching the selectively masked one of the input waveguide and theoutput waveguide to reduce the selectively masked one of the inputwaveguide and the output waveguide to a second height that is greaterthan zero, and less than, but not equal to the first height.
 60. Themethod of claim 59, further comprising forming an upper cladding on theinput waveguide, the output waveguide and the resonator, the uppercladding having the first index of refraction.
 61. The method of claim60, further comprising forming a heating element on the upper claddingthat is configured to alter an optical property of the input waveguide,the output waveguide and the resonator.